For a microphone used in an especially important place such as a conference room or a broadcasting station, a plurality of microphones are often installed at predetermined positions on a desk etc. because it is necessary to take measures against a break of sound caused by a failure of microphone or to individually connect the microphones to many loudspeakers or recorders.
In this case, since a large number of microphones are erected in front of a speaker, an installation space for installing the microphones must be secured, and moreover there arises a problem in that the speaker cannot be seen well from a visual point of view.
For this reason, in some conventional microphones, the number of installed microphones is decreased as far as possible by incorporating two or three systems of microphone units in one microphone housing in order that the installation space can be secured and the speaker can be seen easily.
On the other hand, there is available a narrow directional microphone in which an acoustic tube is attached to the front sound terminal side of a microphone unit having a front and rear sound terminals to make the directivity narrow. Conventionally, the narrow directional microphones having various constructions have been proposed including the narrow directional microphone disclosed in Japanese Patent Application Publication No. S62-118698.
However, in the field of narrow directional microphone, unlike the aforementioned microphone used for conference etc., there is no example in which a plurality of microphone units are housed in one cylindrical microphone case as far as the inventor knows.
As shown in FIG. 2, if narrow directional microphones 3, 3 of independent two systems are housed in one cylindrical microphone case 2 to form a narrow directional microphone body 1, as is apparent from the above-described conventional example, the microphone body 1 is formed by installing a microphone unit 4 having a front acoustic terminal 4a and a rear acoustic terminal 4b so that the rear end of an acoustic tube 5 is attached to the front acoustic terminal 4a side in an enclosed state. Also, the acoustic tube 5 is provided with slit holes 6 in the peripheral wall portion thereof, and the slit holes 6 are covered with an acoustic resistance material 7 so as to provide narrow directivity.
In the case where the narrow directional microphone body 1 is formed in this manner, problems described below arise. The two narrow directional microphones 3 must be arranged in the microphone case 2 with a gap t being provided therebetween to prevent acoustic interference caused, for example, by resonance between the acoustic tubes 5, 5.
Therefore, the size of the microphone case 2 itself increases as shown in FIG. 2, and also the total weight of the microphone body 1 increases because two acoustic tubes 5 are housed in the microphone case 2. Especially when the acoustic tubes 5 are formed of a metallic material, the weight increases remarkably.
Also, in the case where the microphone body 1 having such a large-size construction is attached to a flexible pipe, not shown, that is used as a gooseneck stanchion, the flexible pipe cannot withstand the weight of the microphone body 1, and hence is turned downward by the gravity, so that there is a fear that the microphone body 1 cannot be adjustably moved to a desired position.